1. Field of the Invention
The present invention relates to an image processing method for converting an image.
2. Related Background Art
Among such image processing methods there are already known an electronic platemaking technology employed in the printing industry, and a computerized photographic image processing technology employed in photographic processing laboratories.
As an example, in a case of photoelectrically scanning an original image with a high precision scanner such as a layout scanner or a laser color printer for obtaining a reproduced image, a signal processing unit is inserted in the process for effecting various processes such as density characteristic correction (gamma correction), gradation control, color correction, paste-up, etc., on an input density signal to achieve the following effects:
(1) correction of faded colors of a color film;
(2) shaping of gradation of highlight shadow areas and enhancement of color representation;
(3) salvaging of an image affected by an equipment malfunction or a mistake in photographing or development; and
(4) representation of a creative image, expansion of imaging areas and creation of novel designs.
Such special processes are realized on digital image signals such as density signals or luminance signals obtained by photoelectrically scanning an original film with a high precision color scanner, a color image pickup tube or a color image pickup device such as a CCD.
There are already known certain special processes such as mosaic processing for obtaining regularly arranged mosaics, or posterization or solarization for obtaining an unrealistic gamma curve. However, such processes are insufficient in number for obtaining creative images, expanding image area and creating novel designs in as much variety as it is desired to do. Also there are known a paste-up function and a painting function as achievable using certain equipment such as the DPB 7000 manufactured by Quantel, the Artron 2000 manufactured by Artronix and the Response 300 manufactured by Scitex, but such processes, which the operator performs by adding images to an original image through a coordinate designating device such as tablet or a digitizer, not only requires a considerable time but also is associated with the drawback that the resulting image is affected by the artistic skill of the operator.
In the following there will be explained, as an example, a mosaic process in which a mosaic is composed of 5 pixels in the x-direction and 5 pixels in the y-direction, or of 25 pixels. .The digital image information of a pixel (m, n) will be represented as a(m, n), which is a digital count obtained by A/D conversion of a density signal or a luminance signal or the original film. In the mosaic process, the pixel information a'(m, n) of the reproduced image after said process is derived from the pixel information a(m, n) of the original image by the following relationship: EQU a'(5m-i, 5n-j)=a(5m-3, 5n-3)
wherein i=1, 2, 3 or 4, j=1, 2, 3 or 4 and m and n are natural numbers. In the above-explained relation the central value of a 5.times.5 pixel block is taken as the representative value and is applied to other pixels in the block, but said representative value may be taken from any pixel of said block or may be the average value of the pixels.
Such conventional process of obtaining regularly arranged mosaics is associated with the following drawbacks:
(1) rectangular mosaic blocks are excessively regularly arranged; and
(2) because the pixels in a block are of the same value, information is lost where the original image requires detail or where the original image contains a large amount of high-frequency components; and there is required an improved processing for generating creative images.